Paper 2020/1281
Key Agreement for Decentralized Secure Group Messaging with Strong Security Guarantees
Matthew Weidner and Martin Kleppmann and Daniel Hugenroth and Alastair R. Beresford
Abstract
Secure group messaging protocols provide end-to-end encryption for group communication. Practical protocols face many challenges, including mobile devices frequently being offline, group members being added or removed, and the possibility of device compromises during long-lived chat sessions. Existing work targets a centralized network model in which all messages are routed through a single server, which is trusted to provide a consistent total order on updates to the the group state. In this paper we adapt secure group messaging for decentralized networks that have no central authority. Servers may still optionally be used, but their trust requirements are reduced. We define decentralized continuous group key agreement (DCGKA), a new cryptographic primitive encompassing the core of a decentralized secure group messaging protocol; we give a practical construction of a DCGKA protocol and prove its security; and we describe how to construct a full messaging protocol from DCGKA. In the face of device compromise our protocol achieves forward secrecy and post-compromise security. We evaluate the performance of a prototype implementation, and demonstrate that our protocol has practical efficiency.
Metadata
- Available format(s)
- Category
- Cryptographic protocols
- Publication info
- Preprint. MINOR revision.
- Keywords
- secure messaginggroup messagingdecentralizationforward secrecypost-compromise security
- Contact author(s)
-
maweidne @ andrew cmu edu
mk428 @ cst cam ac uk
dh623 @ cst cam ac uk
arb33 @ cst cam ac uk - History
- 2021-05-31: revised
- 2020-10-14: received
- See all versions
- Short URL
- https://ia.cr/2020/1281
- License
-
CC BY